Aircraft engine particulate matter emissions from sustainable aviation fuels: Results from ground-based measurements during the NASA/DLR campaign ECLIF2/ND-MAX

Targeted Use of Sustainable Aviation Fuel to Maximize Climate Benefits

“…Here, we extend the methodology of Brem et al 19 using the latest measurements from the NASA ACCESS 23 and ECLIF2/ ND-MAX 22,24 (10% < F ̂< 100%) and higher ΔH (up to 1.1%). A piecewise function retains the original formulation at low ΔH (≤ 0.5%), and an exponential term is added when ΔH > 0.5% to ensure that the estimated ΔnvPM EI n asymptotically approaches −100%…”

“…Here, we extend the methodology of Brem et al using the latest measurements from the NASA ACCESS and ECLIF2/ND-MAX , campaigns, which investigated the SAF effects on nvPM EI n under a wider range of engine thrust settings (10% < F ̂ < 100%) and higher Δ H (up to 1.1%). A piecewise function retains the original formulation at low Δ H (≤ 0.5%), and an exponential term is added when Δ H > 0.5% to ensure that the estimated ΔnvPM EI n asymptotically approaches −100% normalΔ normalnvPM EI n [ % ] = { lefttrue ( α 0 + α 1 F̂ ) × normalΔ H , when 0.25em normalΔ H ≤ 0.5 % ( α 0 + α 1 F̂ ) × normalΔ H × e false( 0.5 − normalΔ H false) , when 0.25em normalΔ H > 0.5 % where α 0 = −114.21 and α 1 = 1.06 are the original coefficients from Brem et al F ̂ is approximated by dividing the m ̇ f at mean sea level (MSL) conditions ( m ̇ f MSL ) by the maximum m ̇ f ( m ̇ f,max MSL ) provided by the ICAO EDB .…”

“…For cruise conditions, m ̇ f Cruise is converted to an equivalent m ̇ f MSL using the Fuel Flow Method 2 (FFM2) methodology ṁ normalf MSL = ṁ normalf cruise true( T amb T MSL true) 3.8 ( p MSL p amb ) e 0.2 M 2 where T amb and p amb are the ambient temperature and pressure, respectively; T MSL (288.15 K) and p MSL (101325 Pa) are the standard atmospheric temperature and pressure at MSL, respectively; and M is the Mach number. Equation , also visualized in Figure S3, is evaluated by comparison to ground and cruise measurements from four experimental campaigns: ,,− the coefficient of determination ( R 2 ) and normalized mean bias (NMB) for the measured and estimated ΔnvPM EI n are, respectively, 0.84 and +28% when compared against ground measurements, and 0.83 and −3.2% against cruise measurements (Figure S5).…”

“…In addition to the CO 2 benefits, SAF can also reduce the nonvolatile particulate matter (nvPM) number emissions index (EI n ) by up to 70% − relative to conventional fuels, with the reduction in nvPM EI n varying as a function of engine thrust settings, fuel hydrogen, and aromatic content. , nvPM emissions at cruise altitudes contribute to contrail formation when conditions in the exhaust plume satisfy the Schmidt–Appleman criterion (SAC). − In the soot-rich regime (EI n > 10 13 kg –1 ), the nvPM EI n is positively correlated with the initial contrail ice crystal number and optical depth (τ contrail ) and negatively correlated with the ice crystal size. , Indeed, recent in situ measurements of young contrail properties , found that replacing conventional jet fuel with SAF led to significant differences in the ice number concentration (up to −70%), ice crystal size (+40%), and τ contrail (−52%), and these changes are expected to reduce the contrail lifetime and climate forcing. − However, several studies , estimate that SAF could increase the contrail occurrence by 1–8% because its water vapor emissions index (EI H 2 O ) can be up to 10% higher than that of conventional fuels. ,, While the effects of SAF on contrail occurrence and changes to contrail properties have been measured, the effects of a lower nvPM EI n on the contrail cirrus net radiative forcing (RF) have so far only been quantified with modeling studies: Schumann et al computed a 39% reduction in global annual mean contrail cirrus net RF for a 50% reduction in nvPM EI n ; Bock & Burkhardt and Burkhardt et al found 15 and 50% reduction in the global contrail cirrus net RF, respectively, when SAF is used across the fleet; and Caiazzo et al reported a −4 to +18% change in the contrail net RF over the United States.…”

Combustion, Chemistry, and Carbon Neutrality

“…Mehl et al recently (2022) discussed the influence of alternative jet fuel composition on combustion intermediates, relying on experiments, surrogates, semidetailed kinetic models, and optimization strategies, and pointed out that more validation is needed for certain compounds, including aromatic and naphthenic fuel fractions . Coupling fundamental-level results and approaches with observations from ground-based and flight experiments will further enhance the knowledge on such challenging, multicomponent targets as real aviation fuels and their emission behavior under practical conditions. , …”